Reconfigurable intelligent surface (RIS) has become a promising technology in future 6G communications. Thanks to its high array gain, low cost, and low power consumption, RISs can improve spectral efficiency and reduce power consumption. The RISs widely studied in most existing works are usually passive RISs.Reconfigurable intelligent surface (RIS) has become a promising technology in future 6G communications. Thanks to its high array gain, low cost, and low power consumption, RISs can improve spectral efficiency and reduce power consumption. The RISs widely studied in most existing works are usually passive RISs.